The invention relates to a direct current-supplying circuit for inductances in the form of a bridge circuit with a rectifier with a smoothing capacitor over the one, first bridge diagonal and an inductive load over the other, second bridge diagonal, the two half-bridge branches, lying between the positive and the negative pole of the smoothing capacitor consisting, on the one hand, of the series connection of a first controllable rectifier cell and a first diode lying in the non-conducting direction with respect to a direction of current flow and, on the other, of a second rectifier cell or a second diode also lying in the non-conducting direction with respect to the current flow. A direct current-supplying circuit of this type is suitable particularly as a main power direct dc converter for, in principle, any inductances.
A circuit, known under the name of H bridge, as shown in FIG. 1, starts out from a rectified line voltage, optionally smoothened by a capacitor K, and consists of, in principle, two controlled rectifier cells, such as semiconductor switches V1 and V2, as well as two not controlled diodes D1 and D2. A so-called xe2x80x9cintermediate circuit voltagexe2x80x9d, produced from an electrical network, is connected, as shown in FIG. 1, to a first bridge diagonal at the terminals 1 and 2. An inductive load L lies over the other bridge diagonal between the terminals 3 and 4. Any type of direct current-supplied inductance, such as a magnetic rectifier cell coil or a motor field coil, is conceivable as load L.
As is generally known, the capacitance of the smoothing capacitor K should be designed comparatively large, since this capacitor basically has two different functions. It serves, on the one hand, to decrease the waviness of the direct current obtained, which is caused by the main rectification. On the other hand, quite independently of the preceding, it has the function of absorbing the so-called xe2x80x9cdemagnetizing energyxe2x80x9d of the load L (coil), that is, the magnetic energy fed back to the intermediate circuit over the two diodes D1, D2 each time after the two semiconductor switches V1, V2 are switched off. As a consequence of this double function, both functions or tasks must be taken into consideration during the dimensioning of the capacitor K. Even if, from the point of view of the overall function, a relatively large waviness in the intermediate circuit or even a not-smoothened intermediate circuit voltage would be acceptable or even necessary for minimizing current harmonics in the electrical network, the capacitor K can never be made smaller than necessary for absorbing the magnetic energy in the case of a still acceptable voltage increase.
In the publication DE 197 09 264 A1 (see, in particular, FIG. 1), a circuit arrangement is known for reducing the reactions on the temporal course of the current, taken from the electrical network, in an inductive load. In the case of an inductive load, for example, a motor winding over a rectifier by active filtration of the harmonics of a basic electrical network oscillation over a boost converter, for which, by a suitable pulse-width modulated control of a further, first semi-conductor switch and a capacitor, which lies parallel to the demagnetizing rectifier cell of the diode D1 and the second controlled semiconductor switch V2 of the circuit of FIG. 1, which absorbs the demagnetizing energy of the inductive load L, a diminution of an otherwise required larger so-called xe2x80x9cHochsetstellerdrosselxe2x80x9d (high set adjuster choke) becomes possible. The additional capacitor exclusively has the function of storing the demagnetizing energy from the inductance on an interim basis.
The invention is based upon the problem, on the one hand, of clearly reducing the electrical network feedback and, on the other hand, of clearly decreasing the size of the smoothing capacitor K.
Referring to the direct current-supplying circuit defined above, the invention is defined by the following distinguishing features comprising a direct current-supplying circuit for inductances in the form of a bridge circuit including a rectifier (G) with a smoothing capacitor over a first bridge diagonal (1, 2) and an inductive load (L) over a second bridge diagonal (3, 4), wherein the first bridge diagonal and the second bridge diagonal form two half-bridge branches lying between a positive pole and a negative pole of the smoothing capacitor and comprising a series connection of a first controllable rectifier cell (V1) and a first diode (D1) lying in a non-conducting direction with respect to a direction of current flow; and at least one of a second rectifier cell (V2) and a second diode (D2) lying in the non-conducting direction with respect to the current flow, wherein
a connecting node (1) of the first bridge diagonal, connected with the positive pole of a rectifier (G), is interrupted and a decoupling diode (D3), poled in the nonconducting direction in relation to a current-flowing direction, from the positive to the negative direct current pole of the rectifier, is connected between the two half-bridge branches and wherein
the smoothing capacitor is divided into two separate capacitances (K1, K2), a first of said separate capacitances (K1), a smoothing capacitor, bridges the direct current side of the rectifier (G) and a second of said separate capacitances (K2), is connected over the second half-bridge branch formed by the series connection of the second diode (D2) and the second controllable rectifier cell (V2) and serves as a capacitor for at least partially absorbing the demagnetizing energy of the inductive load (1) to reduce electrical network reactions.
In the invention, the features are such that the connecting node of the first bridge diagonal, connected with the positive pole of a rectifier, is interrupted and a decoupling diode, poled in the nonconducting direction in relation to a current-flowing direction, from the positive to the negative direct current pole of the rectifier, is connected between the two half-bridge branches, and the smoothing capacitor is divided into two separate capacitances, one of which, as smoothing capacitor, bridges the direct current side of the rectifier and the other, is connected over the second half-bridge branch formed by the series connection of the second diode and the second controllable rectifier cell and, at the same time, serves as a capacitor for absorbing, at least partially, the demagnetizing energy of the inductive load, especially to reduce electrical network reactions.
Not only does the invention have the advantage of avoiding the above-mentioned over-dimensioning of the smoothing capacitor K in the circuit arrangement of FIG. 1, but also, of better addressing the increasingly restrictive regulations concerning permissible current harmonics of the electrical network, which can be caused at least partially by such over-dimensioning.